| MISSION_DESCRIPTION |
The descriptions given here were originally copied from the
``Stardust Mission Plan'' document and its addenda (used with
permission from the Stardust project). To reflect the
completion of the primary mission, the information has been
updated by Tony Farnham using the weekly status reports, press
releases and informational bulletins released by the Stardust
mission.
Mission Overview
================
The primary science goal of the STARDUST mission was to collect
Wild 2 coma samples, plus bonus interstellar dust samples, in
aerogel, and return them to Earth. On January 2, 2004, the
spacecraft successfully flew by the comet, obtaining dust
samples that were returned to the Earth on January 15, 2006.
Additional science return was obtained in the form of images of
the comet coma and nucleus obtained with the NAVCAM, in situ dust
composition measurements obtained with the Comet and
Interstellar Dust Analyzer (CIDA) and dust impact counts from
the Dust Flux Monitor (DFMI).
Trajectory
----------
The STARDUST mission was designed for a low velocity (6.1
km/s) flyby of comet Wild 2 during a time when the comet was
moderately active (at a heliocentric distance of 1.9 AU). The
spacecraft was then designed to have a low energy Earth
returning trajectory so that dust samples obtained at the
comet could safely be returned to Earth.
The launch on February 7 1999 put Stardust into a two year
orbit, which would bring it back to Earth for a gravitational
assist in 2001. Deep Space Maneuver #1 (DSM1), broken into
three separate burns, was executed on January 18, 20 and 22,
2000, when Stardust was near aphelion. This maneuver imparted
a 170 m/s deterministic delta-V to set up the orbit for the
Earth flyby, which occurred on January 15, 2001. The Earth
flyby increased the spacecraft's semi-major axis so that
Stardust could reach comet Wild 2. The new orbit had a 2.5
year period. A small, 2.65 m/s, deep space maneuver (DSM2)
was executed on January 24, 2002 to correct for minor
trajectory errors from the previous Earth flyby. On June
17-18, 2003, the third deep space maneuver (DSM3) was
performed to properly target Wild 2. It imparted a Delta-V
of 69 m/s. On January 2, 2004, Stardust encountered Comet
Wild 2 (98.5 days after the comet's perihelion passage),
passing at a distance of 237 km. The last deep space
maneuver, DSM4, was performed in the first week of February
2004. It was a small maneuver (5 m/s) and adjusted the orbit
to target the spacecraft back to Earth so the Sample Return
Capsule could reenter the atmosphere and parachute to the
recovery site in Utah.
Asteroid 5535 Annefrank Encounter
----------------------------------
On November 2, 2002 04:50:20 UTC, Stardust encountered the
asteroid 5535 Annefrank. The encounter distance was 3079 km
and the solar phase angle ranged from 130 deg to 47 degrees
during the period of observations. This encounter was used as
an engineering test of the spacecraft and ground operations in
preparation for the encounter with comet Wild 2.
Comet Encounter
---------------
On January 2, 2004, 19:21:28 UTC, Stardust encountered Comet
Wild 2 (98.5 days after the comet's perihelion passage). The
spacecraft passed the comet on the sunward side with a
relative velocity of 6.1 km/sec. The closest approach
distance was 237 km (+/- 1km). (The original encounter
distance was planned to be 150 km, but this was changed after
a safety review board decided to increase the closest approach
distance to minimize the potential for catastrophic dust
collisions.)
The relative velocity between the comet and the spacecraft was
such that the comet actually overtook the spacecraft from
behind as they traveled around the Sun. During the encounter,
the spacecraft was on the sun-lit side of the nucleus,
approaching at a solar phase angle of 70 degrees, reaching a
minimum angle of 3 degrees near closest approach and departing
at a phase angle of 110 degrees.
Interstellar Dust Collection
----------------------------
The interstellar dust particle (ISP) collection periods
occurred near the first and second aphelion portions of the
spacecraft's orbit, when the relative velocity between the
spacecraft and the ISP streams is at a minimum. In addition
to the favorable velocity alignment, these collection periods
are further defined by the need to avoid large off-Sun
pointing of the solar panels, collection of beta meteoroids,
and deep space maneuvers.
The first ISP collection period lasted from February 22
through May 1, 2000. The second collection period was from
August 5 through December 9, 2002. Although the opportunity
existed for additional ISP collection on the third orbit, this
would have been after the Wild 2 encounter, and it was decided
that it was undesirable to re-open the SRC after the comet
encounter.
In Situ Particle Analysis
-------------------------
CIDA and DFMI experiments were executed at every available
opportunity during the mission. The main constraints on their
operation were the availability of spacecraft power and
conflicts with other mission activities. Prime experiment
periods were defined as those where the interstellar particle
(ISP) streams are oriented to fall within the CIDA
field-of-view.
Earth Return
------------
On January 15, 2006 the Sample Return Capsule (SRC)
successfully separated from the Stardust spacecraft. After
separation, the spacecraft executed a divert maneuver that put
it into a heliocentric orbit, while the SRC re-entered the
Earth's atmosphere and parachuted to the ground. The SRC was
recovered at the Utah Test and Training Range (UTTR) and
transported to the staging area at UTTR for the retrieval of
the sample canister. The canister was then transported to the
planetary materials curatorial facility at Johnson Space
Center in Houston.
Mission Phases
==============
Six mission phases were originally defined for significant
spacecraft activity periods. These were the Launch, Cruise 1,
Earth Gravity Assist, Cruise 2, Wild 2 Encounter, Cruise 3,
and Earth Return. One more mission phase -- Annefrank
Encounter, -- completely nested inside the Cruise 2 phase was
added in 2002 when the asteroid flyby was approved
as a full scale Wild 2 encounter test.
LAUNCH
------
Mission Phase Start Time : 1999-02-07
Mission Phase Stop Time : 1999-03-08
The launch phase began as the launch vehicle lifted-off and
ended with the completion of the activation and checkout of
most of the spacecraft subsystems. Included in this phase
were spacecraft separation from the launch vehicle,
establishment of attitude and communications, tracking of the
spacecraft and the execution of the first trajectory
correction maneuver (TCM-1) to correct the injection error.
The duration of this phase was 30 days.
CRUISE 1
--------
Mission Phase Start Time : 1999-03-08
Mission Phase Stop Time : 2000-11-14
The Cruise 1 phase of the first part of the STARDUST mission,
nearly six years long, was a period of relatively low
activity. This part spanned from launch through the Earth
flyby. Within this phase are embedded the first ISP collection
period and the CIDA and DFMI experiments. The ISP collection
period during this phase of the mission started 380 days after
launch and continued for 69 days.
EARTH GRAVITY ASSIST
--------------------
Mission Phase Start Time : 2000-11-14
Mission Phase Stop Time : 2001-02-14
The Earth flyby was performed primarily to provide a gravity
assist to the STARDUST spacecraft thus reducing the delta-V
requirements of the mission. The flyby changed the orbital
period from 2 years to about 2.5 years. The spacecraft
approached Earth from the dark side with a velocity of 6.5
km/s and receded back into the dark side having flown by the
sunward side at a closest approach altitude of
6008 km. During the flyby the Sun-Earth-spacecraft angle cycled
from ~130 degrees to ~28 degrees at closest approach to a
minimum of ~19 degrees (8 minutes after closest approach) and
back up to ~90 degrees toward the end of the EGA phase. The
Earth flyby time was 15 January 2001 11:14:28 UTC.
CRUISE 2
--------
Mission Phase Start Time : 2001-02-14
Mission Phase Stop Time : 2003-09-24
The Cruise 2 phase was the second part of cruise, spanning the
time between the Earth flyby and the Wild 2 encounter. Within
this phase are embedded the second ISP collection period and
the CIDA and DFMI experiments. The ISP collection period
during this phase of the mission started 1275 days after
launch and continued for 126 days.
ANNEFRANK ENCOUNTER
-------------------
Mission Phase Start Time : 2002-10-31
Mission Phase Stop Time : 2002-11-05
This phase was the part of the mission, during which STARDUST
flew by the S-type, main belt asteroid Annefrank. The
Annefrank flyby occured with just over one month (out of four)
remaining in the second ISP collection period and was fully
embedded with Cruise 2 phase of the mission.
This encounter was not present in the original mission plan and
was added in 2002 as a full scale Wild 2 encounter test.
The main objective and supporting rationale for this test was
to implement the entire Wild 2 encounter sequence in flight
at Annefrank.
The spacecraft flew past Annefrank on 2 November 2002 at
4:51:20 UTC at a closest approach distance of 3079 km. The
imaging sequence encompassed a solar phase angle range from
130 deg to 47 deg.
WILD 2 ENCOUNTER
----------------
Mission Phase Start Time : 2003-09-24
Mission Phase Stop Time : 2004-02-21
The most important mission phase of STARDUST ranged from 100
days before the encounter with comet Wild 2 to 50 days after.
Encounter occurred on January 2, 2004, 19:21:28 UTC.
The primary goal of obtaining comet coma samples during the
encounter flyby was accomplished by a navigation plan that
delivered the spacecraft to a close approach distance of 237
km from the nucleus. Near the closest encounter, the
spacecraft +x-axis was aligned with the S/C velocity vector
relative to Wild 2 so that the dust shield protected the
S/C. In this flyby configuration, the Earth was located in the
direction of the spacecraft +z-axis (also HGA direction). The
spacecraft approached Wild 2 from above and receded below the
comet's orbit plane.
Although the collection of cometary dust samples was the
primary goal of the mission, it is totally passive, enabled by
deployment of the aerogel collector and the setting of the
spacecraft / collector attitude perpendicular to the dust
stream. The collector was deployed on December 24, 2003 and
remained deployed until five hours after the encounter, at
which time the spacecraft should have exited the coma. The
majority of the dust was believed to have occurred in the few
hours around closest approach.
CRUISE 3
--------
Mission Phase Start Time : 2004-02-21
Mission Phase Stop Time : 2005-10-17
The Cruise 3 phase was the third part of cruise, spanning from
the Wild 2 encounter to the return to Earth. During this
period, no dust collection took place. The dust collectors
were stowed to protect the comet particles and to prevent any
potential problems that might endanger their return to the
Earth.
EARTH RETURN
------------
Mission Phase Start Time : 2005-10-17
Mission Phase Stop Time : 2006-01-16
This phase of the mission began 90 days before Earth Return
(ER) and ended when the SRC was transferred to the ground
handling team. Earth approach contained three TCM's and a
final divert maneuver, performed after SRC separation, to
prevent the spacecraft from following the SRC into the Earth's
atmosphere. Prior to separation, the spacecraft was placed at
the separation attitude and the SRC was spun up using a spin
release mechanism. This provided the spin stabilization that
the SRC required for successful atmospheric entry. The SRC
entered the atmosphere at 09:57 UTC on January 15, 2006.
The SRC aeroshell protected the sample canister against
the extreme aerodynamic heating experienced during
atmospheric entry. The aeroshell also removed over 99 percent
of the initial kinetic energy thus allowing the parachute
system to place the SRC within the allowable touchdown
requirements.
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